Survey of Admission Control of Supporting VoIP Services in IEEE 802.11e QoS-enabled WLAN

1. Survey of Admission Control of Supporting VoIP Services in IEEE 802.11e QoS-enabled WLAN R93725003 卓德忠 R93725010 鍾佳芳 2 Jan. 2006

2. Outline • Introduction • Admission Control • Parameterized EDCA • Conclusions

3. Introduction Motivation Introduction of 802.11e features Introduce the reference design of HCCA in 802.11e

4. Motivation • 802.11e is an enhanced QoS support in WLANs • The most promising framework among QoS enhancements of WLANs • The contention-based MAC access scheme is hard to provide quality of service (QoS) assurance for VoIP services.

5. Introduction of 802.11e • IEEE 802.11 WG, “Draft Supplement to Standard for Telecommunications and Information Exchange between Systems-LAN/MAN Specific Requirements — Part 12: Wireless MAC and PHY Specifications: MAC Enhancements for QoS,” IEEE 802.11e/draft 12.0, Nov. 2004. • Qiang Ni,”Performance Analysis and Enhancements for IEEE 802.11e Wireless Networks,” in IEEE Network, July/August 2005

6. Introduction of 802.11e • A new MAC layer function called the hybrid coordination function (HCF) is proposed. • HCF uses a contention-based channel access method, also called enhanced distributed channel access (EDCA) • Polling-based HCF-controlled channel access (HCCA) method • Transmission opportunity (TXOP) refers to a time duration during which a QSTA is allowed to transmit a burst of data frames • EDCA-TXOP • HCCA-TXOP

7. MAC Architecture for QoS L.W Lim, R. Malik, P.Y. Tan, C. Apichaichalermwongse, K. Ando, Y. Harada, “A QoS scheduler for IEEE 802.11e WLANs”, First IEEE Consumer Communications and Networking Conference, 2004. Jan 2004, pp.199 – 204

8. HCCA Features • Different traffic classes called traffic streams (TSs) are introduced in HCCA. • QSTA is not allowed to transmit a packet if the frame transmission cannot finish before the next beacon • TXOPLimitis used to bound the transmission time of a polled QSTA. • In order to initiate a TS connection, a QSTA sends a traffic specification (TSPEC) to the QAP. A TSPEC describes the QoS requirements of a TS • Mean Data Rate, • Nominal MSDU Size • Maximum Service Interval or Delay Bound

9. Reference scheduling algorithm in 802.11e • The schedule for an admitted stream is calculated in three steps. • Calculation of the Scheduled Service Interval (SI). • Calculation of TXOP duration for a given SI • Admission control scheme • Service Interval (SI) • calculates the minimum of all Maximum Service Intervals for all admitted streams. Let this minimum be "m". • chooses a number lower than "m" that is a submultiple of the beacon interval. Ex. MSI1=15ms, MSI2=20ms, beacon interval = 100 =>SI = 10ms

10. Reference scheduling algorithm in 802.11e • Calculation of TXOP duration • Mean Data Rate (ρ) • Nominal MSDU Size (Li) from the negotiated TSPEC • Scheduled Service Interval (SI) calculated in the first step, • Ni: the number of MSDUs that arrived at the Mean Data Rate during the SI

11. Reference scheduling algorithm in 802.11e • Parameters • Nominal MSDU Size (Li) from the negotiated TSPEC • Min Physical Transmission Rate (R), • Maximum allowable MSDU size (M) • Overheads in time units (O): IFSs, ACKs, and CF-Polls • Admission Control

12. Admission Control AC for CBR traffic AC for VBR traffic

13. Survey of Admission Control • Deyun Gao, Jianfei Cai and King Ngi Ngan, “Admission Control in IEEE 802.11e Wireless LANs,”in IEEE Network, July/August 2005 • Admission Control for CBR Traffic • physical-rate-based admission control PRBAC • Admission Control for VBR Traffic • Effective TXOP duration • Variable Service Interval

14. Admission Control for CBR Traffic • Gao, D.; Cai, J.; Zhang, L., “Physical rate based admission control for HCCA in IEEE 802.11e WLANs”, Advanced Information Networking and Applications, 2005. AINA 2005 • physical-rate-based admission control (PRBAC) • long-term average physical rates for admission control • instantaneous physical rates to distribute TXOPs

15. Admission Control for CBR Traffic

16. The maximum numbers of VoIP traffic stream • Woo-Yong Choi, “A Centralized MAC-Level Admission Control Algorithm for Traffic Stream Services in IEEE 802.11eWireless LANs”, International Journal of Electronics and Communications, 2004 • obtain the maximum numbers of VoIP traffic streams that can be admitted to IEEE 802.11a/e, IEEE 802.11b/e and IEEE 802.11g/e wireless LANs for various delay requirements.

17. Arrival Pattern • Di:the constant inter-arrival of burst • Li: burst size, [0, maximum burst size] • Pi: the length of the burst period,

18. Arrival Pattern (cond) • Li: burst size, [0, maximum burst size] • PRi: the peak data rate • MRi: the mean data rate • Pi: the length of the burst period, • Di:the constant inter-arrival of burst

19. Max Queue Size ^ • B: the maximum queue state • Si: constant service rate • Pi: the length of the burst period • PRi: the peak data rate PRi-Si Si

20. Max delay • Ti : the maximum delay • provide the traffic stream with the constant service rate, Si(bits/second). ==> • Admission Control • ΣSi < available service rate (AR)

21. Numerical examples • Burst length Pi = 1.5 sec • Burst inter-arrival time Di = 1 sec • IMBE codec:4.8Kbps • User payload of VoIP MPDU is 88 bits • Number of MPDU = 4.8*1.5/88 = 82 • Burst size Li = 4.8*1.5 + 82*(UDP, IP and MAC) = 7200 + 82*(16 + 224 + 240) = 46560 bits

22. Numerical examples • Peak data rate PRi = Li/Pi = 31Kbps • Mead data rate = PRi*1.5/(1.5+1) = 18.6Kbps • Actual available service rate R • R=11.34Mbps(a, g), 2.2Mbps(b)

23. Numerical examples 5 times About 35 VoIP pairs

24. Admission control for VBR traffic • W.F. Fan, D.Y. Gao, D. H.K. Tsang and B. Bensaou, "Admission Control for Variable Bit Rate traffic in IEEE 802.11e WLANs,” to be appewed in The Joint Conference of 10th Asia-Pacific Conference on Communications and 5th International Symposium on Multi-Dimensional Mobile Communications, Aug. 2004 • introducing Effective TXOP duration (the necessary TXOPs which can statistically guarantee that the packet loss probability is less than a threshold ) • guarantee the packet loss rate

25. Admission control for VBR traffic • W. F. Fan;Tsang, D.H.K.; Bensaou, B., “Admission Control for Variable Bit Rate traffic using variable Service Interval in IEEE 802.1 le WLANs”, ICCCN 2004. Proceedings • using Variable Service Interval • avoid over-guarantee on packet delay (which with large delay bound) • guarantee the packet loss rate • The larger the service interval, the less TXOP durations required

26. Parameterized EDCA Comparison of HCCA and EDCA Admission Control algorithm Resource Allocation algorithm Performance Evaluation

27. Parameterized EDCA • Chun-Ting Chou, Sai Shankar N and Kang G. Shin, “Achieving Per-Stream QoS with Distributed Airtime Allocation and Admission Control in IEEE 802.11e Wireless LANs, “INFOCOM 2005 • Chun-Ting Chou, Kang G. Shin and Sai Shankar, “Distributed Control of Airtime Usage in Multi-rate Wireless LANs,” under review of the IEEE/ACM Transactions on Networking

28. Comparison of HCCA and EDCA • Challenges of HCCA • The HC needs to re-compute the service schedule whenever a new traffic stream is added to, or deleted from a WLAN • When two WLANs using HCCA operate on the same channel, it requires additional coordination between them • 802.11k

29. Comparison of HCCA and EDCA (cont’d) • Challenges of EDCA • A quantitative control of stations’ medium occupancy cannot be achieved via the current EDCA • The link adaptation allows stations to vary their PHY transmission rate based on the link condition makes the airtime usage control even harder

30. AdmissionControl Algorithm • Guaranteed Rate (g) -----------------Appendix A • C is the channel capacity • Dependent on PHY rates • We must consider multi-rate 802.11 environment • airtime ratio(ri,j)

31. AdmissionControl Algorithm • New condition • Overall conditions • EA: Efficient Airtime Ratio

32. Allocation of Airtime • EDCA • Control the TXOP Limit of each stations • Same EDCA parameters • Control the frequency of station’s access to the wireless medium • Same TXOP (access duration)

33. Controlling the TXOP Limit • TXOP • Ni : The number of data frames per one access • Transmission time : Ni Ni Ni

34. Controlling the TXOP Limit(cont’d) • Example • Li = 600, 600, 1200, 1200 bytes • Ri = 48, 48, 48, 24Mbps • Ti =100, 100, 200, 400(TM) sec • ri = 0.1, 0.2, 0.2, 0.1(rM) • Ni = 4, 8, 4, 1

35. Controlling the Access Frequency • TXOP limit • Access frequency approximation[24] [24] Chun-Ting Chou, Kang G. Shin and Sai Shankar, “Distributed Control of Airtime Usage in Multi-rate Wireless LANs,” under review of the IEEE/ACM Transactions on Networking

36. Controlling the Access Frequency(cont’d) • Example • Li = 600, 600, 1200, 1200 bytes • Ri = 48, 48, 48, 24Mbps • Ti =100, 100, 200, 400(TM) sec • Ni = 4, 4, 2, 1 • ri = 0.1, 0.2, 0.2, 0.1

37. 37 Mbps t =35 s N=16 System Efficiency

38. Time-varying Transmission Rates 54Mbps → 24Mbps

39. Conclusion • HCCA • High system efficiency (higher EA) • Contention free • with admission control mechanisms, the delay and packet loss rate of VoIP / other multimedia streams are guaranteed. • However, the influence of Jitter is not discussed here.

40. Conclusion (cont’d) • Parameterized EDCA • No control overhead in overlapping multiple LANs • No adjustment for change • HCCA needs to re-compute schedule • Easy adaptation of extra airtime for the change of station’s PHY rate

41. Reference • IEEE 802.11 WG, “Draft Supplement to Standard for Telecommunications and Information Exchange between Systems-LAN/MAN Specific Requirements — Part 12: Wireless MAC and PHY Specifications: MAC Enhancements for QoS,” IEEE 802.11e/draft 12.0, Nov. 2004. • Qiang Ni,”Performance Analysis and Enhancements for IEEE 802.11e Wireless Networks,” in IEEE Network, July/August 2005 • Deyun Gao, Jianfei Cai and King Ngi Ngan, “Admission Control in IEEE 802.11e Wireless LANs,”in IEEE Network, July/August 2005 • Gao, D.; Cai, J.; Zhang, L., “Physical rate based admission control for HCCA in IEEE 802.11e WLANs”, Advanced Information Networking and Applications, 2005. AINA 2005

42. Reference • W.F. Fan, D.Y. Gao, D. H.K. Tsang and B. Bensaou, "Admission Control for Variable Bit Rate traffic in IEEE 802.11e WLANs,” to be appewed in The Joint Conference of 10th Asia-Pacific Conference on Communications and 5th International Symposium on Multi-Dimensional Mobile Communications, Aug. 2004 • W. F. Fan;Tsang, D.H.K.; Bensaou, B., “Admission Control for Variable Bit Rate traffic using variable Service Interval in IEEE 802.1 le WLANs”, ICCCN 2004. Proceedings • Woo-Yong Choi, “A Centralized MAC-Level Admission Control Algorithm for Traffic Stream Services in IEEE 802.11eWireless LANs”, International Journal of Electronics and Communications, 2004 • Chun-Ting Chou, Sai Shankar N and Kang G. Shin, “Achieving Per-Stream QoS with Distributed Airtime Allocation and Admission Control in IEEE 802.11e Wireless LANs, “INFOCOM 2005 • Chun-Ting Chou, Kang G. Shin and Sai Shankar, “Distributed Control of Airtime Usage in Multi-rate Wireless LANs,” under review of the IEEE/ACM Transactions on Networking

43. Bits Arrival curve : A(t) peak rate : P Guaranteed rate : g mean rate : ρ σ d error Time Appendix A. Guaranteed Rate • Dual-token bucket filter Tokensarrive at Mean Data Rate Tokens arrive at Peak Data Rate Bucket size B = σ (1-ρ/P) Data frames drained at Guaranteed Rate MAC frame buffer Arriving traffic stream